Source: Dungeons & Dragons
Threat Assessment: 7. A beholder is nasty on a stick. A big floating ball of eyes, each eye has a different magical power. The worst is the central eye's anti magic ray. Every moment of battle he's making you weaker as he fills the air with death beams and beams to turn you to stone. Definitely consider running.
Limitations: Nothing really significant.
Personal note: in later versions of the game, beholders became a space faring race meaning there are places in the universe with whole cities of beholders.